And I'm David Greene. There are new developments this morning in the story of the al-Qaida plot to bomb an airplane heading to the United States. It turns out that the man who was thought to be the bomber was actually a double agent - that, according to U.S. officials.

It is quite a spy tale. Intelligence agencies had an agent inside al-Qaida's branch in Yemen and so they were able to foil the plot, and the bomb is now in U.S. hands. To make sense of the story, we're joined by NPR's Dina Temple-Raston. Dina, good morning.

DINA TEMPLE-RASTON, BYLINE: Good morning.

GREENE: So this is getting more dramatic with each day. What can you tell us? What's the latest?

TEMPLE-RASTON: Well, according to several U.S. and foreign intelligence officials familiar with the plot, a foreign intelligence service sent an agent to infiltrate al-Qaida's arm in Yemen, a group called AQAP - al-Qaeda in the Arabian Peninsula. And the intelligence service basically sent this agent to the group with a U.S. visa in his passport. And his instructions were to volunteer for a suicide mission. And AQAP actually took him up on his offer.

And the agent spent weeks with the group, and then AQAP provided him with their latest-generation underwear bomb for his suicide mission. What's interesting about this is that the agent was basically following in the footsteps of the underwear bomber in 2009. The underwear bomber was this young Nigerian who just showed up in Yemen; said he wanted to martyr himself; and ended up on Northwest Flight 253 with explosives in his underwear.

This time, instead of a young Nigerian presenting himself, a double agent did instead.

GREENE: OK. So this double agent shows up and presumably, follows the orders he was given and volunteers; and then actually gets his hands on the bomb that the group had been working on?

TEMPLE-RASTON: Exactly, and that was the first - sort of big intelligence coup. The bomber, who was really a double agent, gets the device; and he turns it over to foreign intelligence services on Monday; and they give it to the FBI for analysis.

It's a lot easier to analyze a bomb when it's intact, rather than after it's exploded. So that's, you know, a big coup. And sources tell us it was a really form-fitting bomb that would have been hard for airport security to spot, even with a pat-down.

To give you an idea of how it's different from the 2009 bomb, the Christmas Day underwear bomb was put in sort of Yemeni boxers - boxer shorts - that are kind of loose fitting. This bomb was put into the equivalent of briefs, so it was much tighter and form-fitting, and harder to see.

GREENE: Interesting. Well, you said, though, that - you know, the FBI getting the bomb was one of the intelligence coups. What were some of the other important moments that you're learning about - the other coups?

TEMPLE-RASTON: Well, we confirmed that there's a link between this plot and the drone strike over the weekend that killed a top al-Qaida operative in Yemen. The person who was killed - his name is Fahd al-Quso - was on the FBI's Most Wanted terrorist list. He was in charge of AQAP's external operations - basically, operations against the West.

And the agent apparently gave the intelligence services the information they needed to target and kill al-Quso. He was also involved in the USS Cole attack, so the U.S. had been hunting him for a while.

GREENE: You know, Dina, one of the frightening things here is that if this group thought they were handing over a bomb that was ready for a suicide mission - the bomb was, presumably, ready to be used, to be deployed - I mean, the FBI has this bomb now to study, but do U.S. officials think that there are more bombs out there?

TEMPLE-RASTON: Well, they haven't ruled that out, but they said that there is no indication so far, to tell them that there are more bombs. It's unclear whether the agent would have known if there were other attacks being planned by other operatives anyway. Officials said that for operational security, AQAP would probably have kept the plans separate and discreet.

We did confirm, though, that the bomb was the work of AQAP's master bomb maker. He's a Saudi, and his name is Ibrahim Hassan al-Asiri. Apparently, the double agent said the bomb was made by him. And al-Asiri is about 29. He's been at AQAP for six years. And the U.S. has had him at the top of their target list, 'cause they're concerned he's teaching others how to make bombs that are hard to detect. And that's why the U.S. has been so eager to get hold of Asiri.

GREENE: All right, we'll be watching this story very closely. Dina, thanks so much.

TEMPLE-RASTON: You're welcome.

GREENE: That's NPR's Dina Temple-Raston, with the latest on the foiled plot to bomb an airliner headed to for the United States. Transcript provided by NPR, Copyright NPR.